Capacitors are widely used in semiconductor technology. They may be used, for example, for noise decoupling, for blocking direct current, and for charge storage in radio-frequency (RF) and analog applications. Semiconductor capacitors typically take the form of diffusion capacitors, trench capacitors, gate capacitors, and metal-insulator-metal (MIM) capacitors. Typically, these devices depend on an insulating layer, frequently silicon dioxide, to form the dielectric between the terminals of the capacitor. Like other layers in a semiconductor device, these dielectric layers are continuously scaled in order to make devices smaller, to increase performance, and to reduce cost of production. As dielectric layers are scaled, especially when scaled faster than the voltage or power supply level, premature punch-through, breakdown, and other dielectric damage is frequently encountered. As a result, obtaining highly-reliable, high-value capacitors becomes increasingly more challenging.
Adding to this challenge is the fact that integrated circuits must frequently be designed to work within a wide range of operating voltages. For example, an integrated circuit may need to work within a power supply voltage range from 1.2 volts to 3.6 volts. This is especially true when a designer wishes that a device be compatible with both modern and older semiconductor technologies.
One way to resolve the problem of voltage-induced dielectric damage in semiconductor capacitors is to simply connect two or more capacitors in series. With this configuration, the voltage drop across any one of the capacitors is reduced and, correspondingly, the reliability of that capacitor is maintained. Nevertheless, maximum total capacitance for a given array of capacitors is achieved by wiring the capacitors in parallel. As a result, it is most advantageous to wire an array of capacitors in parallel when the power supply voltage is low enough that capacitor reliability is not adversely affected. This allows the circuit to have the maximum total capacitance for a given area. Conversely, when the power supply voltage is high enough to adversely affect capacitor reliability, it is usually advantageous to wire the array of capacitors in series to such an extent that reliability is maintained at the cost of reduced total capacitance. Accordingly, in those integrated circuits that are used over a wide range of power supply voltages, it is desirable to be able to selectively and dynamically modify the wiring configuration of capacitors depending upon the level of power supply voltage.